The present invention relates to a floor panel structure of a vehicle body, particularly to a floor panel structure of a vehicle body in which a floor of an automotive vehicle is formed by a floor panel coupled to a plurality of frame members which extend in substantially longitudinal and width directions of the vehicle body.
It is known that vibration from frame members coupled to the engine or the suspension of the vehicle is transmitted to floor panels and makes the floor panels and air in the cabin vibrate, resulting in uncomfortable vibration and noises being generated in the cabin. Herein, the vibration of engine itself and the road noise from the suspension are considered as vibration resources primarily. The road noise is generally caused by resonance of vehicle tires and sympathetic vibration of the suspension.
Conventionally, damping materials or the like which are applied to the floor panels or the particular portions of the vehicle body have been generally used to suppress such vibration and noises. However, a large amount of these materials are generally required, and thereby the weight of the vehicle body tends to increase improperly. This overweight would cause various disadvantages including an issue of costs.
Meanwhile, in view of facts that the frequency of uncomfortable vibration transmitted from the engine and suspension in the automotive vehicle is generally less than 400 Hz and particularly the peak of road noises exists at around 250 Hz which is caused by the resonance of vehicle tires, it is also known that the peculiar frequency of floor panels can be shifted to a high frequency band more than 400 Hz by increasing the rigidity of floor panels with many beads formed at the panels or thicker panels. Namely, the uncomfortable vibration and noises can be suppressed, by preventing the floor panels from vibrating sympathetically with the suspension or the vehicle tires.
In this case, however, the vibration with relatively high frequency tends to increase improperly instead. Accordingly, in order to suppress properly the increased vibration with relatively high frequency at the same time, additional damping materials or the like which should be useful to such vibration with high frequency would be also required. Accordingly, the same problems as described above would occur inevitably.
Meanwhile, Japanese Patent Laid-Open Publication No. 6-107235 discloses a panel structure of a vehicle body in which a panel comprises a plurality of projecting portions with shell structure, which has a proper strength in bending, compressing and tensioning, and recess portions extending between the projecting portions. Herein, the vibration generated could be increased at the recess portions primarily, and the increased vibration could be reduced properly by damping materials provided at the recess portions.
In general, since the exhaust pipe, various auxiliary parts and the like are disposed below or on the floor panel, the above-described projecting portions formed at the floor are required to be disposed with their proper height and location which will not interference with these objects. Further, the height of the projecting portions needs to be set properly so as to provide the passengers with comfortable stepping. Also, those projecting portions need to be formed properly within floor panels enclosed by the frame members. However, in view of these limitations in vehicle-body structure or manufacturing, there exists some cases where the vehicle body panel structure disclosed in the above-described patent publication could not reduce the vibration properly.